Conventionally, nappies (known also as diapers) comprise an absorbent pad sandwiched between a layer of non-woven fabric permeable to liquids, and a layer of impermeable material such as polyethylene. Also included, usually between the pad and the layer of non-woven fabric, is a fluid distribution layer, widely referred to as an acquisition layer, or acquisition-distribution layer (ADL).
Nappies are substantially rectangular in appearance, and present an anatomically contoured central section.
The pads likewise are of substantially rectangular outline, and aligned centrally on the nappy.
The aforementioned pads are formed generally in the aspirating pockets or cavities of a drum, rotatable about a horizontal axis and fed at a point on its periphery with a flow of absorbent material.
The flow of material consists predominantly of synthetic and/or natural fibrous particles and may also contain superabsorbent polymer (SAP) powders blended homogeneously with the fibrous particles.
In prior art units, the cylindrical surface of the drum on which the pads take shape is surmounted by a hood, occupying a sector of predetermined length, into which the flow of absorbent material is fed pneumatically from the top.
Likewise in prior art units, whether the flow of material contains fibrous particles only, or a blend of fibrous particles and superabsorbent polymer powders, the inside of the hood may also accommodate the outlet of a feed duct from which discrete quantities of superabsorbent polymer powders are dispensed.
The dispensing action is produced generally by intermittently operated valve means, and under pressure, in such a way that a circumscribed central area of the pad will be loaded with the SAP material.
In one prior art solution, such valve means take the form of a rotating disc furnished with one or more substantially rectangular arcuate openings through which the flow of SAP material is directed intermittently, as the disc rotates, through the feed duct and into the hood, and ultimately into the cavities of the drum in which the pads are formed.
Using the valve means described above, it is not possible to obtain a uniform distribution of the discrete quantities of SAP material within the circumscribed area of application.
Moreover, it is not possible to guarantee a precise geometrical shape for the circumscribed area of application when using such valve means.